Post, courier, forwarding and other mail services, which enable people to exchange documents and data, have been widely used both in the past and at the present time. With the evolution of modern technology, the use of electronic dispatch devices and systems, such as modems, facsimile machines, electronic mail (E-Mail) and EDI systems, computers, communication networks, and so forth, to exchange data and documents is rapidly evolving.
A substantial quantity of the information exchanged, such as contracts, purchase orders, invoices, monetary orders, notices, and even warning and notification messages, are of utmost importance. Sometimes, when a dispute arises between the sending and receiving party of the exchanged information, the receiving party may raise the claim that he never received the information, that the received information was different from what the sender claims to have sent, or the receiving party may even attempt to forge the received information.
The need, therefore, arises for the sender to prove that specific information has been sent at a specific time to that specific receiving party.
Various solutions to various related problems have been proposed in the literature. For example, the transmission operation itself may be authenticated, as shown in U.S. Pat. No. 5,339,361 (Schwalm et al.), which describes a communication system providing a verification system to identify both the sender and recipient of electronic information as well as an automatic time stamp for delivery of electronic information. This patent, however, does not verify the dispatched information.
Document authentication methods, for example by notarization, have long been in use. A method for notarization of electronic data is provided by EP-A-516 898 (PITNEY BOWES INC.) or its patent family member U.S. Pat. No. 5,022,080 (Durst et al.) which authenticates that source data has not been altered subsequent to a specific date and time. The method disclosed includes mathematically generating a second unit of data from the first unit of data, as by CRC generation, parity check or checksum. The second unit of data is then encrypted together with a time/date indication, and optionally with other information to form an authentication string. Validation that the first unit of data has not been changed is provided by comparing the original data's authentication string with the authentication string generated from the data and time in question. A method is even suggested for having the recipient verify the authenticity of the sender, the time of transmission and the data.
Other patents which discuss document authentication are U.S. Pat. Nos. 5,136,646 and 5,136,647 both to Haber et al. According to these patents, a unique digital representation of the document (which is obtained by means of a one-way hash function) is transmitted to an outside agency, where the current time is added to form a receipt. According to U.S. Pat. No. 5,136,647, the receipt is certified using a cryptographic digital signature procedure, and is optionally linked to other contemporary such receipts thereby fixing the document's position in the continuum of time. According to U.S. Pat. No. 5,136,646, the receipt is certified by concatenating and hashing the receipt with the current record catenate certificate which itself is a number obtained by sequential hashing of each prior receipt with the extent catenate certificate.
Various cryptographic schemes are known in the prior art for encrypting and for authenticating digital data and/or its author. For example Symmetric algorithms such as DES [1.01] and IDEA [1.02], one-way hash functions [1.03] such as MD5 [1.04], Public-Key (asymmetric) algorithms [1.05] such as RSA [1.06], and verifiable digital signatures generation algorithms [1.12] such as DSA [1.07] or RSA, as well as combinations thereof such as PGP [1.08] and MACs [1.13], are currently widely used for security and for authentication purposes [1.09]. An excellent publication relating to encryption, authentication, public-key cryptography and to cryptography and data security in general, as well as applications thereof and additional references to multiple sources can be found in [1]. Further prior art, in particular referring to integrity of stored data, can be found in D. W. Davies & W. L. Price "Security for computer networks", 1989, John Wiley & Sons, Chichester (UK).
Proof of delivery of non-electronic documents is provided, for example, by Registered Mail and courier services. It is commonly used to authenticate the delivery of materials at a certain time to a certain party, and serves as admissible proof of delivery in a court of law. However, no proof is provided as to the information contents of the specific dispatch.
E-mail and other electronic messages forwarding services are commonly used today. The sender sends a message to the dispatching service which, in turn, forwards the message to the destination and provides the sender with a delivery report which typically includes the date and time of the dispatch, the recipient's address, the transmission completion status, and sometimes even the transmitted data, the number of pages delivered, the recipient's identification information, and so on. The provided delivery report mainly serves for accounting purposes and for notifying the sender of the dispatch and/or its contents. Moreover, frequently no record of the specific dispatched data is maintained with the service after the delivery is completed or provided to the sender.